Background

In 2016 the Department of Conservation received funding to control pigs in 7019 ha in Waipoua forest, Northland. Pigs are known to have detrimental effects on forest systems by potentially changing soil properties and affecting seedling turnover. Pigs may also be a vector of kauri phytophlera (Phytophlera agathidicida) and pig control is hoped to reduce the spread of kauri dieback and to protect kauri stands.
A pig control programme will start in earnest in June 2016 and it is proposed to control 7019 ha within Waipoua forest on an annual basis. Monitoring changes in pig disturbance is a requirement of the programme. It is unknown how any pigs are in the management area and there is likely to be high reinvasion of pigs from the surrounding forest. Monitoring changes to the proportion of pig disturbance (“rooting”) within the management area is one way to measure of the output of the control programme. Pig control and pig disturbance monitoring are not common in New Zealand and there are few good examples of robust monitoring programmes. This monitoring plan and sample design is largely based on pig disturbance monitoring undertaken by Auckland City in 16000ha of the Waitakere Ranges to monitor changes in response to a sustained programme of pig control (Krull, 2012 & Krull et al. (2016); Krull et al., 2013). Additional information will be collected on the hunting programme itself as a measure of the effort spent, such as the location and number of kills, hours and days spent hunting. Pig disturbance monitoring is planned to begin in June 2016 at the same time as pig control is planned to start. Pig disturbance monitoring is most sensitive in winter months because of the soft ground (Krull pers comm.).

Monitoring protocol

Methodology

Pig disturbance will be sampled by measuring the proportion of “fresh” and “old” pig disturbance along 8 - 10 permanently located transects in three monitoring “blocks” that are all nearly the same size to there is equal probabilities of selection between blocks so valid estimates for pig disturbance can be made.

Rules for transect establishment

Observers must complete the randomly located monitoring points/transects in the order they are selected. This has the advantage that the number of transects monitored can be differ between the monitoring blocks and yet the data remain compatible. However, observers should aim for a minimum of 8 transects per monitoring block.
Dividing the management area into three monitoring blocks will reduce the travel time between the sample points enabling more transects to be established. The long travel time between transects was a significant reason why the number of transects were reduced in the Waitakere Ranges.
If observers choose to measure transects in spatial order to increase efficiency, they must be sure that all transects can be completed. For example, if sample points 1, 4 and 5 are spatially close together and sample points 2 and 3 are close together, observers may measure 1, 4 and 5 in that order, but only if they are sure that they can also complete 2 and 3 as well.

When to abandon a sample point

Each monitoring block will have 5 “oversample” points. These are “backup” sample points if the starting point of a transect is deemed unsafe. Observers must abandon it and move to the next random point on the list. Only if a transect is abandoned for other compelling reasons may the oversample be used. Not using all of the planned sample, in the given order, can seriously undermine the robustness of the study. Transects can be abandoned if they occur in unsafe terrain. Simply move to the next ordered point on the list.
At least 50m or more of a transect must be measured for the transect to be included in the sample design. If observers encounter bluffs, river crossings or other reasons where observer safety or accessibility is compromised, the observer can turn the transect 90 degrees (magnetic) as per the NPCA RTC and DOC’s Tier 1 monitoring protocols and continue until 100m is reached.
If less than 50m of transect can be measured, then it should be abandoned and observers move to the next randomly selected point on the list.

Marking transects

Run all transects on a random bearing that has already been generated for each transect.
Observers must travel to the random start point, GPS and permanently mark the start and end points with permolat or other permanent markers and scratch (or write) the monitoring block, transect number and compass bearing on them. * Clearly mark the path travelled using flagging tape or other means along the compass bearing.
Follow the transect bearing as accurately as possible. Clearly mark any 90 degree turns with permolat and scratch (or write) the metres reached and compass bearing.
Record all transect location details, any directional changes (metres along transect and compass bearing) in the datasheets (Appendix 1 and 2).

Transect measurements

The overall measurement objective is to measure the proportion (m) of “fresh” pig disturbance and “old” pig disturbance along 100m transects and to repeat this every 12 months.
Classifying pig disturbance by age is important because this will measure the immediate impact of pig reductions by measuring change in “fresh” disturbance (within 12 months). This “fresh” disturbance will transition into “old” disturbance, which should show an overall reduction over the following 24 months (disturbance can be recognisable for up to 18 months) (Cheryl Krull pers comm.).
Both age categories can be combined to give an overall proportion of pig disturbance.

See Appendix 1 and 2 for datasheets and examples of datasheets.

What to measure on transects

GPS and permanently mark the beginning of a transect and walk 100m at the random bearing that has already been allocated for each sample point. Look for evidence of pig disturbance 1m either side of the transect line (ie a 2m wide swath). When pig disturbance is observed, “project” the length of the disturbance onto the transect line and measure the length to the nearest 0.1m. See Figure 2 below (modified from Cheryl Krull). In this diagram there are two disturbance events. Disturbance 1 is 2.5m long and disturbance 2 is 1.2m long.

Figure 2. Demonstrating how to “project” the length of the disturbance on the transect and measure the length in metres to the nearest 0.1m.

Fresh vs Old disturbance

Disturbance must be categorised as “fresh” or “old” and it is important to consistently apply the age categories so monitoring can detect a real change in each categories as well as the overall change in disturbance.
A photographic guide is provided below to distinguish fresh from older disturbance (Figures 3, 4 and 5) (images courtesy of Cheryl Krull).

Figure 3. Fresh disturbance - moist and free of leaves.

Figure 4. Old disturbance - dried out and leaf litter present.

Figure 5. Old disturbance - presence of seedling growth in disturbance patch.

What else to record along transects (see Appendix 1 and 2)

Record a description of the general vegetation along the transect especially the occurrence of kauri.
Record any special features of the transect that might help observers re-measure it accurately next time.
Photograph any interesting evidence of pig disturbance along the transect. It is not necessary to relocate the same pig disturbance event in each measurement.

Resources

The following resources are required;

Map of pig control area with random sample points.
Grid references of sample points inclusing oversample points.
100m and/or several 20m tape measures to measure transect length.
Hip chain (optional.)
5m builders tape to measure disturbance.
Permolat to mark start and end points and any direction changes.
Coloured flagging tape.
Permanent markers.
Clip boards.
Compass.
GPS.
Pen/pencils/Permanent marker pen
Camera.
Recording sheets (see the ‘Data Sheets’ tab)

Sample design

Objective:

To monitor the results of pig (Sus scrofa ) control in the core area of the pig management area in Waipoua Forest as part of efforts to control the spread of Kauri dieback disease.

Target population

A written description of the population intended for monitoring

Pig impacts in the Core Area of the Waipoua Forest Pig management Area

Sample frame

A spatial representation of the target population

Shapefile depicting the Core Area of the Waipoua pig management area

Sample design

Monitoring transects have been located within the sample frame using the Balanced Acceptance Sampling (BAS) method. BAS allocates points in a spatially, balanced random order within the sample frame. Monitoring sites must be visited according to the spatially balanced sequence, the ‘sampleID’. In order to accomodate field constraints the Core Area sample frame has been divided into 3 roughly equal size areas and monitoring transects created in 3 ‘Groups’. Transects must be measured according to the order in the ‘sampleID’ in each ‘Group’. If a transect must be missed for reasons of access or safety then the next transcet in the ordered list must be used. 10 transects have been provided in each group as the initial sample. If needed, more transects are available from the oversample, although these must still be used according to the ordered list.

The transects from the sample and the oversample can be viewed below.

The shapefile for the transects can be downloaded below:

The data for the start and end point of the transects, including the random bearing, can be downloaded from the table below.

Data sheets

Results

Pig disturbance in the core area of Waipoua Forest is low (0.58±2.51) when compared to the 3.7% measured by Krull (2012). Disturbance is clustered on 25% of the transects (Fig. 1). More years of data collection is required to assess change in pig disturbance levels as a result of pig culling efforts.

Figure 1. Distribution of pig disturbance and percent disturbance/transect on monitoring transects in Waipoua Forest.

Waipoua Forest Park

Monitoring design and protocols for assessing the effectiveness of Pig (Sus scrofa) control

Background

Background

Monitoring protocol

Methodology

Transect measurements

Resources

Sample design

Objective:

Target population

Sample frame

Sample design

Data sheets

Results

Results

References